6. Performance test of a mini ice plant (Lecture) 1. The The Ice Ice Mak Maker icemaker er,, ice generato generator r, or ice machine machine may An icemak may refer efer to eith either er a consumer device for makin ice! found inside a home free"er# a stand$alone appliance for makin ice! or an industrial machine for makin ice on a lare scale. The term %ice machine% usually refers to the stand$alone appliance. The ice enerator is the part of the ice machine that actually produces the ice. This &ould include the evaporator and any associated drives'controls'suframe that are directly involved &ith makin and eectin the ice into storae. *hen most people refer to an ice enerator! they mean this ice$ makin susystem alone! minus refrieration. refrieration. An ice machi machine! ne! ho&ev ho&ever! er! partic particula ularl rly y if descri descried ed as +pack +packae aed+! d+! &ould &ould typically e a complete machine includin refrieration and controls! re,uirin only connection to utilities. The term icemaker is more amiuous! &ith some manufacturers manufacturers descriin descriin thei theirr pack packa aed ed ice ice mach machin ine e as an icem icemak aker er!! &hil &hile e othe others rs desc descri rie e thei theirr enerators in this &ay. -. Princ Principl iple e of ice makin makin refrigeration equipments equipments are All refrigeration are made made of four four key comp compon onen ents ts## the the evaporator! the condenser! the compressor and the throttle valve. Ice machines all &ork the same &ay. The function of compressor is to compress lo&$pressure refrierant vapor to hih$pressure vapor! and deliver it to the condenser. ere! the hih$pressure vapor is condensed into hih$pressure li,uid! and drained out throuh the throttle valve to ecome lo&$pressure lo&$pressure li,uid. At this point! the li,uid is conduc conducted ted to the evapor evaporato ator! r! &her &here e heat heat e/cha e/chani nin n occurs occurs!! and ice is created. This is one complete refrieration cycle. 0. Indus Industri trial al icemak icemakers ers ommer ommercia ciall ice ice cue cue makers makers impro improve ve the the ,ualit ,uality y of ice y usin usin movin movin &ater. &ater. The &ater is run do&n a surface that is constantly at 2 3 (0- 34) ecause only &ater &ithout impurities &ill free"e at this temperature on a surface. *ater &ith impurities re,uires lo&er temperatures to free"e and &ill continue to &ash do&n do&n the surfa surface ce and throu throuh h the the drain drain of a commer commercia ciall icema icemake kerr. Air and undissolved solids &ill e &ashed a&ay to such an e/tent that in hori"ontal evaporator machines the &ater has 57 of the solids removed! resultin in very hard! virtually pure! clear ice. In vertical evaporators the ice is softer! more so if there there are are actual actual indivi individua duall cue cue cells. cells. ommer ommercia ciall ice ice machin machines es can can make make di8erent si"es of ice like 9akers! crushed! cue! octaon! and tue. *hen the sheet of ice on the cold surface reaches the desired thickness! the sheet is slid do&n onto a rid of &ires! &here the sheet+s &eiht causes it to e cut into the desired shapes! after &hich it falls into a storae in. :. 4la 4lake Ice Ice Flake Flake ice is prod produc uced ed y appl applyi yin n &ate &aterr to the the insi inside de or outs outsid ide e of a refrierated drum or to the outside of a refrierated disk. The drum is either vertical or hori"ontal and may e either stationary or ;/ed. The disk is vertical and rotates aout a hori"ontal a/is.
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Ice removal devices fracture the thin layer of ice produced on the free"in surface of the ice maker! reakin it free from the free"in surface and allo&in it to fall into an ice in! &hich is enerally located elo& the ice maker. The thickness of the ice produced y 9ake ice machines can e varied y adustin the speed of the rotatin part of the machine! varyin evaporator temperature! or reulatin the &ater 9o& on the free"in surface. 4lake ice is produced continuously! unlike tuular and plate ice! &hich are produced in an intermittent cycle or harvest operation. The resultin thickness ranes from 1 to :.< :.< mm. mm. A cont contin inuo uous us oper operat atio ion n (&it (&itho hout ut a harv harves estt cycl cycle) e) re,ui e,uirres less less refrieration capacity to produce a kiloram of ice than any other type of ice manufacture &ith similar makeup &ater and evaporatin temperatures. The e/act amount of refrieration refrieration re,uired re,uired varies y the type and desin of the 9ake ice machine. Typical 9ake ice machines are sho&n in 4iures 1 and -.
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All &ater used y 9ake ice machines is converted into ice# therefore! there is no &ast &aste e or sp spil illa lae e.. 4lak 4lake e ice ice mak makers ers are are us usua uall lly y oper operat ated ed at a lo& lo&er evaporatin temperature than tue or plate ice makers! and the ice is colder &hen it is removed from the icemakin surface. The surface of 9ake ice is not &etted y tha&in durin removal from the free"in surface! as is common &ith other types of ice. =ince it is produced at a colder temperature! 9ake ice is most adapta adaptal le e to autom automate ated d stora storae! e! parti particul cularl arly y &hen &hen lo&$te lo&$tempe mperat ratur ure e ice is desired.
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The rapid free"in free"in of &ater on the free"in surface entrains air in the 9ake ice! ivin it an opa,ue appearance. 4or this reason! 9ake ice is not commonly used used for applic applicati ations ons &her &here e clear clear ice is import important ant.. *her *here e rapid rapid coolin coolin is important! such as in chemical processin processin and concrete concrete coolin! 9ake ice is ideal ecause the 9akes present the ma/imum amount of coolin surface for a iven amount of ice. *hen used as inredient ice in sausae makin or other food rindin and mi/in! 9ake ice provides rapid coolin &hile minimi"in mechanical damae to other inredients and &ear on mi/in' cuttin lades. =ome 9ake ice machines can produce salty ice from sea&ater. These are particularly useful in shipoard applications. >ther 9ake ice machines re,uire addin trace amounts of salt to the makeup &ater to enhance the release of ice from the refrierated surface. In rare cases! the presence of salt in the ;nished product may e oectionale. oectionale. <. Tuul uular ar Ice Ice Tubular ice is produced y free"in a fallin ;lm of &ater either on the outside of a tue &ith evaporatin refrierant on the inside! or on the inside of tues surrounded y evaporatin refrierant on the outside. Outside Tube . *hen ice is produced on the outside of a tue! the free"in cycle is normally from to 1< min! &ith the ;nal ice thickness from < to over 10 mm follo&in the curvature of the tue. The refrierant temperature inside the tue continually drops from an initial suction temperature of aout $:3 to the terminal suction temperature in the rane of $1- to $-63. At the end of the free free"i "in n cycl cycle! e! the the cir circula culati tin n &ate &aterr is shut shut o8! o8! and and hot hot disc discha har re e as as is introduced to harvest the ice. To maintain proper harvest temperatures! typical dischare as pressure is 1.1 MPa. This drives the li,uid refrierant in the tue up into an accumulator and melts the inside of the tue of ice! &hich slides do&n throu throuh h a si"er si"er and mechan mechanica icall reak reaker! er! and ;nally ;nally do&n do&n into into stora storae. e. The defrost cycle is normally aout 02 s. The unit returns to the free"in cycle y returnin the li,uid refrierant to the tue from the accumulator. This type of ice maker operates &ith refrierants refrierants ?$@1@! ?$@1@! ?$:2:A! ?$<2@! and ?$--. ?$1- may e found in some older units. iher capacity units of 5 M per -: h and larer usually use ?$@1@. The capacity of the unit increases as the terminal suction pressure decreases. A typical unit &ith -13 makeup &ater and ?$@1@ as the refrierant produces 1@.< M of ice per -: h &ith a terminal suction pressure of -6< kPa and re,uires 1-6 k* of refrieration. This e,uates to @.- k* of refrieration per mearam of ice. The same unit produces 0@.@ M of ice per -: h &ith &ith a ter termina minall suct suctio ion n pres pressu surre of 1: 1:< < kPa kPa and and re,ui e,uirres - -2 2 k* of refrieration. This e,uates to @.< k* of refrieration per mearam of ice. 4iure 0 sho&s sho&s the physica physicall arran arranem ement ent for an ice ice maker maker that that makes makes ice on the outside of the tues.
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Inside Tube. *hen ice is produced inside a tue! it can e harvested as a cylinder or as crushed ice. The free"in cycle ranes from 10 to -6 min. The tue is usually -2 to <2 mm in diameter! producin a cylinder that can e cut to desired desired lenths. lenths. The refrier refrierant ant temperatu temperature re outside outside the tue is continua continually lly droppin! droppin! &ith an initial temperature of $:3 and a terminal suction temperature temperature ranin from $@ to $-23. At the end of the free"in cycle! the circulatin circulatin &ater is <
shut shut o8 and the ice is harves harvested ted y intr introd oduci ucin n hot dischar dischare e as into the refri refrier erant ant in the the free" free"in in sectio section. n. To mainta maintain in as as temper temperatu ature re!! typica typicall dischare as pressure is 1.- MPa. This releases the ice from the tue# the ice descends to a motor$driven cutter plate that can e adusted to cut the ice cylinders to the lenth desired (up to :2 mm). At the end of the defrost cycle! the dischare as valve is closed and &ater circulation resumes. These units can use refrierants ?$@1@ ?$@1@ and ?$--# ?$1- may e found in older units. Aain! the capacity increases as the terminal suction pressure decreases. A typical unit &ith -13 makeup &ater and ?$@1@ as the refrierant produces 05 M of ice per -: h &ith a terminal suction pressure of -@< kPa and re,uires -6k* of refrieration. This e,uates to <2 k per kiloram of ice. The same unit produces 62 M of ice per -: h &ith a terminal suction pressure of -12 kPa and re,uires :@< k* of refrieration. This e,uates to 6: k per kiloram of ice. Tuular Tuular ice makers are advantaeous ecause they produce produce ice at hiher suction pressures pressures than other types of ice makers. makers. They can make relatively thick and clear ice! &ith curvatures that help prevent ridin in storae. Tuular ice makers have a reater heiht re,uirement for installation than do plate or 9ake ice makers! ut a smaller footprint. Provision must e made in the refrieration system hih side to accommodate the volume of refrierant re,uired for the proper amount of harvest dischare as. Ice temperatures are enerally hiher than the temperature of 9ake ice makers. Supply Water. =upply &ater temperature has a reat e8ect on the capacity of either type of tuular ice maker. If the supply &ater temperature is reduced from -1 to :3! the ice production of the unit increases appro/imately 17. In larer larer system systems! s! the econom economics ics of preco precooli olin n the &ater &ater in a separa separate te &ater &ater coolin system &ith hiher suction pressures should e considered. 6. Plate Ic Ice Plate ice makers are commonly de;ned as those that uild ice on a 9at vertical surface. *ater *ater is applied aove free"in free"in plates and 9o&s y ravity over the free"in plates durin the free"e cycle. Li,uid refrierant at a temperature et&een $-1 and $@3 is contained in circuitin circuitin inside the plate. The lenth of the free" free"in in cycle cycle over overns ns the thickn thickness ess of ice prod produce uced. d. Ice thick thicknes nesses ses in the rane of 6 to -2 mm are ,uite common! &ith free"e cycles varyin from 1- to :< min. min. 4iur iure e 11 sho& sho&s s a 9o& 9o& dia diara ram m of a plat plate e ice ice mak maker usin usin &ate &aterr for for harves harvest. t. All plate plate ice ice makers makers use use a sump sump and recir recircul culati atin n pump pump concep concept! t! &here &herey y an e/ces e/cess s of &ater &ater is applie applied d to the free" free"in in surfa surface. ce. *ater ater not conver converted ted to ice on the plate is colle collecte cted d in the sump sump and recirc recircula ulated ted as precooled &ater for ice makin.
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@. ue ice Cube ice machines are classi;ed as small ice machines! in contrast to tue ice machines! 9ake ice machines! or other ice machines. ommon capacities rane from 02 k (66 l) to 1!@<< k (0!65 l). =ince the emerence of cue ice machines in the 15@2s! they have evolved into a diverse family of ice machines.
ue ue ice machin machines es are are common commonly ly seen seen as vertic vertical al modula modularr device devices. s. The upper part is an evaporator! and the lo&er part is an ice in. The refrierant circulates inside pipes of sale$contained evaporator! &here it conducts the heat e/chane &ith &ater! and free"es the &ater into ice cues. *hen the &ater is thorouhly fro"en into ice! it is automatically released! and falls into the ice in. The ice in can also e e,uipped &ith compressors.B&hyCD compressors.B&hyCD Eenerally Eenerally cue ice machines &ith over 0-2 k (@12 l) capacities have uilt$in compressors in the ice in for storae prior to sales! for use &hen demands are lare. ue ice is created in a cuic shape! &ith each ede usually et&een 1< and 0< mm (5F1 (5F16 6 and and 1 0F 0F in). in).Th The e su surf rfac ace e area area of ever every y ton ton of cue cue ice ice is appro/imately appro/imately 1!00 m- (1:!52 s, ft). . omp omprresso essors rs Most compresso compressors rs are either either positive positive displacem displacement ent compresso compressors rs or radial radial compressors. compressors. Positive displacement compressors compressors are currently currently the most eGcient type of compres compressor sor!! and have the larest larest refrie refrierati ratin n e8ect per sinle sinle unit (:22H-<22 T?). They have a lare rane of possile po&er supplies! and can e 02 ! 1222 1222 ! or even even hiher hiher.. The The princ principl iple e ehin ehind d positi positive ve displ displac aceme ement nt compressors utili"es a turine to compress refrierant into hih$pressure vapor. Positive displacement compressors are of four main typesJ scre& compressor! rollin piston compressor! reciprocatin compressor! and rotary compressor. =cre& compressors can yield the larest refrieratin e8ect amon positive displacem displacement ent compres compressors sors!! &ith their refrie refrierati ratin n capacity capacity normally normally ranin ranin from <2 T? to :22 T?. =cre& compressors also can e divided to sinle$scre& type and dual$scre& type. Kual$scre& type is more often seen in use ecause it is very eGcient. ?ollin ollin pis piston ton compr compress essors ors and recip recipro rocat catin in compr compress essors ors have have simil similar ar refrieratin e8ects! and ma/imum refrieratin e8ect can reach 622 k*. ?ecip eciprrocat ocatin in comp comprresso essors rs are are the the most most comm common on type type of comp comprresso essorr ecause the technoloy is mature and reliale. Their refrieratin e8ect ranes
from from -.- k* to -22 k*.Bfu k*.Bfurther rther e/planatio e/planation n neededD neededD They compress compress as y utili"in a piston pushed y a crank shaft. ?otary compressors! mainly used in air conditionin e,uipment! have a very lo& refrieratin e8ect! normally not e/ceedin < k*. They &ork y compressin as usin a piston pushed y a rotor! &hich spins in an isolated compartment. 5. on ondens ensers ers All condensers can e classi;ed as one of three typesJ air coolin! &ater coolin! or evaporative coolin. An air coolin condenser uses air as the heat conductin media y lo&in air throuh the surface of condensers! &hich carries heat a&ay from the hih$ pressure! hih$temperature refrierant vapor. A &ater &ater coolin coolin conden condenser ser uses uses &ater &ater as the heat heat conduc conductin tin media media to coolin refrierant vapor to li,uid. An evaporative condenser cools the refrierant vapor y usin heat e/chane et&een the evaporator pipes and the evaporated &ater &hich is sprayed on the surface of the pipes. This type of condenser is capale of &orkin in &arm environments# they are also very eGcient and reliale. •
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